Cell surface membranes are to be studied with serological and physical techniques. The mobility of surface proteins, especially the glycoprotein strong transplantation antigens, will be studied by forming mouse-human heterokaryons and following redistribution of antigens in the membranes of these cells. Mobility may also be followed by techniques of fluorescent labelling, bleaching and recovery. Serological analysis of embryo cells and teratocarcinoma cells will be performed using microcytotoxicity tests and immunofluorescence in an attempt to learn of surface antigens uniquely expressed, or altered during development of the embryo. Antisera are to be raised in syngeneic mice against teratoma cells to aid in this typing. Studies of the binding of labelled hormone, glucagon, to liver cell membranes will be continued in order to determine the effect of genes linked to the major histocompatibility complex on cell responses to polypeptide hormones. BIBLIOGRAPHIC REFERENCES: Edidin, M., Zagyansky, Y. and Lardner, T. (1976) Measurement of membrane protein lateral diffusion in single cells. Science 191, 466-468. Zagyansky, Y. and Edidin, M. (1976) Lateral diffusion of concanavalin A receptors in the plasma membrane of mouse fibroblasts. Biochim. Biophys. Acta 433, 209-214.